Add missing since tags for new API

Change-Id: I90d4d7566b2e220b8ea8ea1c644fe4b7fa81c0a3
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/transport/HMACSHA1NonceGenerator.java

@@ -56,6 +56,8 @@
 
 /**
  * The nonce generator which was first introduced to git-core.
+ *
+ * @since 4.0
  */
 public class HMACSHA1NonceGenerator implements NonceGenerator {
 

org.eclipse.jgit/src/org/eclipse/jgit/transport/NonceGenerator.java

@@ -49,6 +49,8 @@
  * A NonceGenerator is used to create a nonce to be sent out to the pusher who
  * will sign the nonce to prove it is not a replay attack on the push
  * certificate.
+ *
+ * @since 4.0
  */
 public interface NonceGenerator {